A simple and workable definition of a drug is any chemical or biologic substance that affects the body and its processes. U.S. law defines a drug as a substance intended for use in the diagnosis, cure, relief, treatment, or prevention of disease or intended to affect the structure or function of the body. (Oral contraceptives are an example of drugs that affect the function of the body rather than a disease.) This comprehensive definition of a drug, although important for legal purposes, is rather complex for everyday use.

Some people incorrectly use the word drug to mean only a substance that produces a pleasurable sensation. Drug abuse—the excessive and persistent use of mind-altering substances without medical need—has accompanied the appropriate medical use of drugs throughout recorded history. Some drugs with potential for abuse have legitimate medical purposes, and others do not.

DrugsSections (A-Z)

Administration and Kinetics of Drugs

Drug administration is the giving of a drug by one of several means (routes). Drug kinetics (pharmacokinetics) describes how the body handles a drug and accounts for the processes of absorption, distribution, metabolism, and elimination.

Adverse Drug Reactions

In the early 1900s, German scientist Paul Ehrlich described an ideal drug as a "magic bullet." Such a drug would be aimed precisely at a disease site and would not harm healthy tissues. Although many new drugs are aimed more accurately than their predecessors, none of them, as of yet, hit the target exclusively.

Brand-Name and Generic Drugs

Drugs often have several names. When a drug is first discovered, it is given a chemical name, which describes the atomic or molecular structure of the drug. The chemical name is thus usually too complex and cumbersome for general use. Next, a shorthand version of the chemical name or a code name (such as RU 486) is developed for easy reference among researchers.

Over-the-Counter Drugs

Overview of Drugs

A drug is defined by U.S. law as any substance (other than a food or device) intended for use in the diagnosis, cure, relief, treatment, or prevention of disease or intended to affect the structure or function of the body. (Oral contraceptives are an example of drugs that affect the function of the body rather than a disease.) This comprehensive definition of a drug, although important for legal purposes, is rather complex for everyday use. A simpler but workable definition of a drug is any chemical or biologic substance that affects the body and its processes.

Also of Interest

Test your
knowledge

Which of the following best describes drug bioavailability?

How a drug is introduced into the body
How the drug is chemically altered by the body
How quickly and how much of a drug reaches its intended target (site) of action
How a drug moves to and from the blood and various tissues of the body

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